Light pollution as a new threat to pollination

Artificial light disrupts nocturnal pollination and leads to a reduced number of fruits produced by the plant. This loss of night time pollination cannot be compensated by diurnal pollinators. The negative impact of artificial light at night on nocturnal pollinators might even propagate further to the diurnal community, as ecologists of the University of Bern were able to show.

The number of bees and other diurnal pollinators is declining worldwide – due to diseases, introduced parasites, pesticides, climate change and the continuing loss of habitats. Now, Eva Knop’s team from the Institute of Ecology and Evolution at the University of Bern, shows for the first time, that nocturnal pollinators can be affected by artificial light leading to a disruption of the pollination service they provide. “So far, nocturnal pollinators have been largely neglected in the discussion of the worldwide known pollinator crisis”, says Knop. However, there are numerous nocturnal pollinators, and they play an important role for plants, as the study in the Bernese Prealps shows. Knop’s team found out, that flowers on meadows which were experimentally illuminated with street lamps are visited around two thirds less frequently by pollinators, than those that were on meadows without any light sources in the vicinity. This has an effect on the fruit set, and therefore the reproduction of plants. The study has now been published in the magazine “Nature”.

“In our modern industrialized society, artificial lighting is nearly ubiquitous. Our results suggest that this widespread exposure to outdoor lights during nighttime hours could represent a novel risk factor for breast cancer,” said lead author Peter James, assistant professor at Harvard Medical School’s Department of Population Medicine at Harvard Pilgrim Health Care Institute, who did the work while a research fellow in the Departments of Epidemiology and Environmental Health at Harvard Chan School.

Previous studies have suggested that exposure to light at night may lead to decreased levels of the hormone melatonin, which can disrupt circadian rhythms—our internal “clocks” that govern sleepiness and alertness—and, in turn, lead to increased breast cancer risk.

The new study, the most comprehensive to date to examine possible links between outdoor light at night and breast cancer, looked at data from nearly 110,000 women enrolled in the Nurses’ Health Study II from 1989-2013. The researchers linked data from satellite images of Earth taken at nighttime to residential addresses for each study participant, and also considered the influence of night shift work. The study also factored in detailed information on a variety of health and socioeconomic factors among participants.

Women exposed to the highest levels of outdoor light at night—those in the top fifth—had an estimated 14% increased risk of breast cancer during the study period, as compared with women in the bottom fifth of exposure, the researchers found. As levels of outdoor light at night increased, so did breast cancer rates.